Breast cancer affects more women than any other cancers in the western hemisphere. The etiology of the majority of human breast cancers is unknown. To identify the etiologic agents and risk factors involved breast cancers, this project will test the hypothesis that environmental carcinogen exposures may contribute to human breast cancers. DNA adducts will be measured and compared in surgical specimens of breast tissue from 150 breast cancer patients and 75 non-cancer controls by the 32P-postlabeling method. DNA adduct profiles will be compared between cases and controls, and between subgroups among cases, e.g. smokers versus non-smokers and women consume a high fat diet versus those with a low fat diet. To explore the potential sources of exposure related to adducts detected in breast tissues, possible exposure will be assessed by epidemiologic approaches. Information on dietary history, smoking, occupation, and alcohol consumption will be obtained from each subject by a self-administered questionnaire. A 10 ml blood sample will be obtained from 50 cases to determine whether lymphocytes can be used as a surrogate. DNA adducts will be measure in lymphocytes and mammary epithelial cells exposed to a carcinogen in culture in 50 cases and 50 controls to determine whether sensitivity to carcinogen exposure is a risk factor for breast cancer. A major adduct which was detected in 40% of breast cancer patients but none of the controls will be identified by comparing with adduct profiles generated in microsomal reaction, cell culture, and tissue culture systems. Since DNA adduct formation and consequent gene mutation are believed to be the key events in chemical carcinogenesis this project will test the hypothesis that the frequency and spectrum of p53 gene mutation is related to adduct formation and may reflect exposure to specific etiologic agents. p53 mutation in tumors of the 150 cases will be determined by single strand conformation polymorphism assay and direct DNA sequencing. The mutation data will be evaluated in relation to the DNA adduct status and the epidemiologic information. These studies are designed to explore the role of environmental carcinogens in human breast cancer development and t define candidate carcinogens and their sources in the environment. Such information is important in identifying etiologic factors in human breast cancers and in finding new strategies for primary prevention of breast cancer